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By Clayton A. Chan, D.D.S. – Founder/Director of Occlusion Connections™
Read my scientific article: “A Review of the Clinical Significance of the Occlusal Plane: Its Variation and Effect on Head Posture” – published in the International College of Craniomandibular Orthopedics Anthology, 2007.
Dentistry is both an art as well as a science. Combining the artistry of tooth position, orientation, embrasure spaces (open or closed), occlusal plane position and arch shape development are all examples of the subjective clinical decision making (“non science”, yet scientific) that must conform to good principles and universal laws of form and function. Implementing one’s judgment, clinical experience in addition to a keen visual eye does not lessen ones position of being objective and clinically sound, especially in the arena of neuromuscular occlusion, orthodontics and restorative/prosthetic care.
There are basic laws in nature and science to support such and so it is the same when establishing the occlusal plane. There is nothing wrong neither is it any less than scientific with using leveling tools (e.g Fox Occlual Plane Analyser, face bows, leveling tables and photos) to help the clinician and technician visualize and capture the maxillary occlusal plane with a normalized head position as long as they are used properly. Subjective is certainly required when it comes to the art of dentistry, yet balanced with the physiologic neuromuscular sciences that can measure muscle function using EMG and CMS technology. I like to use all the scientific tools available in dentistry in addition to applying my artistic mind to create postural form for healthy function.
Depending on boney landmarks alone as references to establish maxillary relationships is almost similar to using jaw joints to reference the mandible/bite. The astute clinician recognizes that neuromuscular and physiologic paradigms reference to healthy muscles not bones which often present with distortions, torques, skews and asymmetries. Repeated studies have shown that relaxed muscles can change the profile and soft tissue architecture over the hamular notch regions. Studies have also shown that relaxed cervical neck musculature with isotonic mandibular muscles will effect head posture and the occlusal plane, thus testing the occlusal plane teaching paradigms as to how these boney landmarks are actually referenced to horizontal level in a physiologic position, not pathologic (“level”).
Labs will say they mount the case to HIP, but will often not dare finish the case to these references because of their experience and realization that this mount will lead to long toothy looking smiles. The technicians realize that the maxilla is not naturally oriented in that manner, thus they make the decision to change the cant of the cast purposely to avoid remakes and an undesirable result for the dentist. The maxillary cast mount should be determined by the dentist, but reality shows that the lab technicians will subjectively and artistically alter the doctors HIP recording to one that is more subtable for finishing the restorative case.
A flat/level HIP mount leads to a pathologic referenced position. A slanted/angled HIP mount is what nature designed physiologically. I advocate the second HIP mount (slanted or angled) which nature intends and is similar to Campers plane or ala tragus plane. This will lead to golden proportions not only in the anterior regions, but also will result in a more idealized crown to root ratio of both the upper to lower posterior molar regions. (Interesting to note that with the classic HIP mount it is often observed that the upper posterior molar crowns will typically look short (staulky) with longer looking lower molar crowns (This is not gold proportions, but results when the maxilla is erroneously mounted to a pathologic relationship). Neuromuscular science supports natures golden proportions and recognizes pathologic distortions! I prefer not to use the fence post and incisive pin as my mounting references to orient the HIP.
Note: A)Pathologic neck posture: Kyphosis resulting in a more flatter occlusal plane. B) Physiologic neck posture: Lordosis resulting in a normalized occlusal plane (angled slant).
If we were to establish boney maxillary cast references such as the hamular notch and incive papilla as some prefer to dogmatically advocate as scientifically objective and mount the maxillary cast to those references the dentist and technician will ultimately be reproducing an undesireable relationship (often resulting in a maxillary cast occlusal plane that appears level and often with the anterior incisal edges vertically upward relative to the posterior teeth). This does not truly represent what nature intended as dental health. Although this idea may appear to be simple to learn and easy to teach this maxillary cast mounting method is in fact one that ignores natures isotonic neutral head position. What we clinicians want to do is replicate healthy relationships of the head, neck and mandible as it relates to the cranum and not pathologic relationship when treating our patients occlusion.
The Fox Plane technique I advocate is a simple means to subjectively analyze and capture what nature intended (an angled HIP mount not flat or level). This is well supported by literature and the orthodontic and prosthetic community. It is a convenient way to capture a proper maxillary recording when the patient is stable and ready to move to the next phase of restorative dentistry. (The classic face bow also works, but is historically more complex and involved and not laboratory friendly). Objective science will always advocate healthy form to support healthy function. The neuromuscular minded clinician needs to learn to use their best judgement skills and understanding and not rely solely on pathologic boney references as their guide. “Nature does not think in mechanical terms”. We need to learn from nature, its beauty,design, form and how it functions.
“Clinicians and dental laboratory technicians have found it important to DIAGNOSTICALLY identify HIP plane so that the dentist does not restore to a distorted cranial base. Since the patient poplulation with chronic TMD and postural problems obviously has a higher than normal HIP plane variance from normal base plane parameters, it is important that the clinician does not replicate this distorted base. Ergo Hoc Proctor Hoc, if clinicians restore this patient using the HIP reference it will only replicate the anatomic manifestations of the etiologic problems.” – Robert Jankelson, Summer 2005 .
To Read the complete published article: http://occlusionconnections.com/wp-content/uploads/Review-of-the-Clinical-SignificanceBW-v12.pdf
Read more click the following links:
- Dr. Chan’s Articles
- GNM Optimized
- Occlusal Plane
- USING THE FOX OCCLUSAL PLANE – 3 STEPS
- What Angle is the Occlusal Plane Relative to the Horizon?
- Which Occlusal Plane Do You Understand – Don’t Be Confused
- Fox Plane and HIP Plane Mounting Considerations
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